UPDATE: U.S. officials say the bomber has been identified as a member of a Hizballah cell.

In the absence of firm evidence, the strongest argument for Iranian involvement in the bombing of a busload of Israeli tourists at a Bulgarian airport is this: The blast came 18 years to the day after the car bombing of a Jewish community center in Buenos Aires, an attack Argentine authorities traced to Iran and Hizballah, the proxy force it established in Lebanon.

Despite its notorious reputation as a state sponsor of terror, the Islamic Republic of Iran has not been much in the terror business for more than a decade. And its recent efforts to return to operational form have been less than impressive. The world was incredulous that a terror mastermind of Tehran’s renown could be traced by a bank transfer to the effort of a Corpus Christi car salesman to enlist a Mexican drug gang to bomb the Saudi ambassador at a Washington restaurant. Since then, Iranian agents have been tracked and arrested plotting in Georgia, Azerbaijan, India, Cyprus, Kenya and Thailand, where things did not go well at all. There, a Thai prostitute’s cell phone would produce a photo of the plotters posing with girls in their arms and water pipes at their sides a week before the bomb they were making blew the roof off their Bangkok apartment. One of the suspects lost a leg when the explosives he was carrying fell at his feet and exploded, not far from where he’d chucked another charge at a taxi after the driver refused to pick him up.

“All signs point towards Iran,” Israeli prime minister Benjamin Netanyahu said two hours after Wednesday’s attack, though those signs remain entirely circumstantial, and the circumstances girdle the globe. Consider, for instance, that the bomb that exploded in the Iranians’ Bangkok flat was the “sticky” kind, attached to a magnet that Thai officials said the conspirators planned to affix to the passing car of an Israeli diplomat. That’s what Iranian agents managed to do a day earlier in New Delhi, injuring the wife of a defense attaché as she went to pick up her kids at school. Significantly, sticky is the kind of bombs that Israeli agents have used in Tehran, where at least three Iranian nuclear specialists have been killed in covert operations that Western intelligence sources have told TIME are, in fact, conducted by the Mossad.

Still, like the anniversary of the Buenos Aires attack, which killed 85 people, what actually links Iran to the Bulgaria bombing is supposition. “It’s very hard to say. Right now we have no clues, no information,” a senior Israeli intelligence official tells TIME. “By process of elimination, we exclude Hamas and Islamic Jihad. They aren’t capable of such an operation so far away [from the Palestinian territories]. There’s also Al Qaeda, but they’re preoccupied with other arenas at the moment. Low chance.

“So it leaves us with the probability of Hizballah alone, or Iran alone, or a joint operation. Which makes sense.”

Hizballah and Iran worked together in Buenos Aires, according to Argentine authorities. They also combined two years later on the last spectacular attack linked to Tehran: The 1996 suicide truck bombing of the Khobar Towers in Saudi Arabia, which killed 19. Though not technically terror because the target was military, the attack was in line with Iranian doctrine on “asymmetrical warfare.” Despite its oil wealth and sovereignty, the Islamic Republic has cast itself as David against Goliath since a 13-year-old boy named Hossein Famideh stopped an Iraqi tank by rolling under it and detonating a belt of grenades, stopping an enemy advance early in the Iran-Iraq war. The boy is celebrated in murals across Iran, including one overlooking official Friday Prayers at Tehran University, and counted by some as the first modern suicide bomber.

Asymmetrical warfare is promoted most publicly by Hasan Abbasi, a former Revolutionary Guards chief who now runs a think tank (he’s on Facebook!). The approach is promoted across the spectrum, from cyber warfare (a web search finds Abbasi seated prominently at the second Cyber Hizballah conference) to naval doctrine. It’s why the Revolutionary Guards invested heavily not in battle ships, but in small speed boats, which swarm and harass the mammoth U.S. vessels patrolling the Strait of Hormuz — and not without success. Earlier this week, American gunners on a Navy supply ship near the strait killed what turned out to be an Indian fisherman approaching so fast they feared he was a suicide bomber. As the head of the Guards’ naval forces put it five years ago, urging militia forces to emulate Famideh: “Even small operations can produce huge effects in the strategic strait of Hormuz and the Persian Gulf.”

One element of the Bulgaria case that gives analysts pause is the news that it appears to have been carried out by a suicide bomber, a young, long-haired seemingly Caucasian man seen loitering by the buses awaiting the arrival of the Israeli tourists, then climbing aboard after them dressed in Bermuda shorts. According to Bulgarian officials, he carried a fake Michigan drivers license. Martyrdom operations on civilian targets are simply far more common among Sunni extremists, and both Hizballah and Iran are Shi’a.

“I’m a bit puzzled; this is not normally the way they do it,” says Benedetta Berti, a terrorism expert at the Institute for National Security Studies in Tel Aviv.[UPDATE: It’s unclear whether the bomber meant to die. The backpack containing the explosive charge may have detonated prematurely as he tried to place it in the luggage space beneath the bus.] On the other hand, Berti tells TIME, Hizballah and Iran may well have opted to try something new after racking up such a long string of failures in the last year or so. After repeatedly missing “hard targets” such as Israeli diplomats, the temptation to do something, somewhere, may have carried the day. “In my time you were always left to your own devices,” a onetime foreign operative for the Iranian security services tells TIME. “These [screw]-ups that you mention might be a generational thing–new guys too young to have been blooded in the war and other activities of the time, thus lacking a whole range of instincts and capabilities that you only get when you have real skin in the game.”

Both Iran and Hizballah have skin in one game: the rapidly deteriorating situation of the Syrian regime headed by Bashar Assad. Under the Assads, Syria has been absolutely vital as the go-between linking Iran and the militia it created in Lebanon, which borders Syria. Add Hizballah’s vow to, at some point, avenge the 2008 assassination by the Mossad of its terror mastermind, Imad Mugniyah, and it’s not hard to make the case that Iran and Hizballah deserve to be suspected first for the seven deaths in Burgas. But it won’t win them much respect.

“As things go very wrong in Syria, you do want to project power,” Berti says. “And if you’re also failing to hit the embassy in Uzbekistan, it kind of takes away from your clout – especially after the “Divine Victory” of 2006 [Hizballah’s perceived stalemate against Israel in the Second Lebanon War]. But you can’t really restore it by attacking tourists at a resort in Eastern Europe.”

Karl Vick has been TIME's Jerusalem bureau chief since 2010, covering Israel,the Palestine territories and nearby sovereignties. He worked 16 years at the Washington Post in Nairobi, Istanbul, Baghdad, Los Angeles and Rockville, MD.